Add an option to noise suppression to generate a new track?

From the readme, noise suppression operates directly on the selected audio track. I feel like it'd be nice if there was an advanced option to have it generate a separate track, so I could do a side-by-side comparison with the original.

Audacity locks up for a while if I have to ctrl-z a big change to a long track, but deleting the new track in case I set it to be too aggressive in suppressing noise is much faster.

Start with the README's noise-suppression documentation and trace the entry point for the effect. Confirm how a processed result can be created as a separate track while preserving the original, then verify that the new track can be deleted independently and that side-by-side comparison remains possible.

Written by the indexing model from the issue text.